<?php

/**
 * @file
 * Database interface code for MySQL database servers.
 */

/**
 * @ingroup database
 * @{
 */

class DatabaseConnection_mysql extends DatabaseConnection {

	/**
	 * Flag to indicate if we have registered the nextID cleanup function.
	 *
	 * @var boolean
	 */
	protected $shutdownRegistered = FALSE;

	public function __construct(array $connection_options = array()) {
		// This driver defaults to transaction support, except if explicitly passed FALSE.
		$this->transactionSupport = !isset($connection_options['transactions']) || ($connection_options['transactions'] !== FALSE);

		// MySQL never supports transactional DDL.
		$this->transactionalDDLSupport = FALSE;

		$this->connectionOptions = $connection_options;

		// The DSN should use either a socket or a host/port.
		if (isset($connection_options['unix_socket'])) {
			$dsn = 'mysql:unix_socket=' . $connection_options['unix_socket'];
		}
		else {
			// Default to TCP connection on port 3306.
			$dsn = 'mysql:host=' . $connection_options['host'] . ';port=' . (empty($connection_options['port']) ? 3306 : $connection_options['port']);
		}
		$dsn .= ';dbname=' . $connection_options['database'];
		// Allow PDO options to be overridden.
		$connection_options += array(
				'pdo' => array(),
		);
		$connection_options['pdo'] += array(
				// So we don't have to mess around with cursors and unbuffered queries by default.
				PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => TRUE,
				// Because MySQL's prepared statements skip the query cache, because it's dumb.
				PDO::ATTR_EMULATE_PREPARES => TRUE,
				// Force column names to lower case.
				PDO::ATTR_CASE => PDO::CASE_LOWER,
		);

		parent::__construct($dsn, $connection_options['username'], $connection_options['password'], $connection_options['pdo']);

		// Force MySQL to use the UTF-8 character set. Also set the collation, if a
		// certain one has been set; otherwise, MySQL defaults to 'utf8_general_ci'
		// for UTF-8.
		if (!empty($connection_options['collation'])) {
			$this->exec('SET NAMES utf8 COLLATE ' . $connection_options['collation']);
		}
		else {
			$this->exec('SET NAMES utf8');
		}

		// Set MySQL init_commands if not already defined.  Default Drupal's MySQL
		// behavior to conform more closely to SQL standards.  This allows Drupal
		// to run almost seamlessly on many different kinds of database systems.
		// These settings force MySQL to behave the same as postgresql, or sqlite
		// in regards to syntax interpretation and invalid data handling.  See
		// http://drupal.org/node/344575 for further discussion. Also, as MySQL 5.5
		// changed the meaning of TRADITIONAL we need to spell out the modes one by
		// one.
		$connection_options += array(
				'init_commands' => array(),
		);
		$connection_options['init_commands'] += array(
				'sql_mode' => "SET sql_mode = 'ANSI,STRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER'",
		);
		// Set connection options.
		$this->exec(implode('; ', $connection_options['init_commands']));
	}

	public function queryRange($query, $from, $count, array $args = array(), array $options = array()) {
		return $this->query($query . ' LIMIT ' . (int) $from . ', ' . (int) $count, $args, $options);
	}

	public function queryTemporary($query, array $args = array(), array $options = array()) {
		$tablename = $this->generateTemporaryTableName();
		$this->query(preg_replace('/^SELECT/i', 'CREATE TEMPORARY TABLE {' . $tablename . '} Engine=MEMORY SELECT', $query), $args, $options);
		return $tablename;
	}

	public function driver() {
		return 'mysql';
	}

	public function databaseType() {
		return 'mysql';
	}

	public function mapConditionOperator($operator) {
		// We don't want to override any of the defaults.
		return NULL;
	}

	public function nextId($existing_id = 0) {
		$new_id = $this->query('INSERT INTO {sequences} () VALUES ()', array(), array('return' => Database::RETURN_INSERT_ID));
		// This should only happen after an import or similar event.
		if ($existing_id >= $new_id) {
			// If we INSERT a value manually into the sequences table, on the next
			// INSERT, MySQL will generate a larger value. However, there is no way
			// of knowing whether this value already exists in the table. MySQL
			// provides an INSERT IGNORE which would work, but that can mask problems
			// other than duplicate keys. Instead, we use INSERT ... ON DUPLICATE KEY
			// UPDATE in such a way that the UPDATE does not do anything. This way,
			// duplicate keys do not generate errors but everything else does.
			$this->query('INSERT INTO {sequences} (value) VALUES (:value) ON DUPLICATE KEY UPDATE value = value', array(':value' => $existing_id));
			$new_id = $this->query('INSERT INTO {sequences} () VALUES ()', array(), array('return' => Database::RETURN_INSERT_ID));
		}
		if (!$this->shutdownRegistered) {
			// Use register_shutdown_function() here to keep the database system
			// independent of Drupal.
			register_shutdown_function(array($this, 'nextIdDelete'));
			$shutdownRegistered = TRUE;
		}
		return $new_id;
	}

	public function nextIdDelete() {
		// While we want to clean up the table to keep it up from occupying too
		// much storage and memory, we must keep the highest value in the table
		// because InnoDB  uses an in-memory auto-increment counter as long as the
		// server runs. When the server is stopped and restarted, InnoDB
		// reinitializes the counter for each table for the first INSERT to the
		// table based solely on values from the table so deleting all values would
		// be a problem in this case. Also, TRUNCATE resets the auto increment
		// counter.
		try {
			$max_id = $this->query('SELECT MAX(value) FROM {sequences}')->fetchField();
			// We know we are using MySQL here, no need for the slower db_delete().
			$this->query('DELETE FROM {sequences} WHERE value < :value', array(':value' => $max_id));
		}
		// During testing, this function is called from shutdown with the
		// simpletest prefix stored in $this->connection, and those tables are gone
		// by the time shutdown is called so we need to ignore the database
		// errors. There is no problem with completely ignoring errors here: if
		// these queries fail, the sequence will work just fine, just use a bit
		// more database storage and memory.
		catch (PDOException $e) {
		}
	}

	/**
	 * Overridden to work around issues to MySQL not supporting transactional DDL.
	 */
	protected function popCommittableTransactions() {
		// Commit all the committable layers.
		foreach (array_reverse($this->transactionLayers) as $name => $active) {
			// Stop once we found an active transaction.
			if ($active) {
				break;
			}

			// If there are no more layers left then we should commit.
			unset($this->transactionLayers[$name]);
			if (empty($this->transactionLayers)) {
				if (!PDO::commit()) {
					throw new DatabaseTransactionCommitFailedException();
				}
			}
			else {
				// Attempt to release this savepoint in the standard way.
				try {
					$this->query('RELEASE SAVEPOINT ' . $name);
				}
				catch (PDOException $e) {
					// However, in MySQL (InnoDB), savepoints are automatically committed
					// when tables are altered or created (DDL transactions are not
					// supported). This can cause exceptions due to trying to release
					// savepoints which no longer exist.
					//
					// To avoid exceptions when no actual error has occurred, we silently
					// succeed for MySQL error code 1305 ("SAVEPOINT does not exist").
					if ($e->errorInfo[1] == '1305') {
						// If one SAVEPOINT was released automatically, then all were.
						// Therefore, clean the transaction stack.
						$this->transactionLayers = array();
						// We also have to explain to PDO that the transaction stack has
						// been cleaned-up.
						PDO::commit();
					}
					else {
						throw $e;
					}
				}
			}
		}
	}
}


/**
 * @} End of "ingroup database".
 */
